Notes: The Ultimate version of this character is not an alternate identity of the regular Marvel character as the Ultimate universe is a distinct reality.
As proven in the "Ultimate Doom" miniseries, in the Ultimate universe, there also exists a Nathaniel Essex working for the Roxxon company. Therefore it is unknown what this Sinister's real name is.
See here for more information.
#46 - 'The Tempest: Part 1' #47 - 'The Tempest: Part 2' #48 - 'The Tempest: Part 3' #49 - 'The Tempest: Part 4' #63 - 'Magnetic North: Part 3' #65 - 'Magnetic North: Part 5' #81 - 'Cliffhangers' #90 - 'Apocalypse: Part 1' #91 - 'Apocalypse: Part 2'